This invention relates to cigarette manufacture, and more particularly to a cigarette-making machine of the type having means for conveying a rod of tobacco made up of a dumping beam (otherwise known as a suction rod conveyor) comprising a porous band moving longitudinally, on the underside of which the rod is formed and moved, being held by suction, as well as means for disposing a strip of paper about the rod of tobacco.
The part of the cigarette-making machine which forms and conveys the tobacco rod by suction on a moving porous band has been disclosed, particularly in commonly assigned U.S. Pat. No. 5,003,996 and in copending, commonly-assigned U.S. Pat. application Ser. No. 07/717,937, filed Jun. 20, 1991, now U.S. Pat. No. 5,168,882. The same applies to the part where the rod is wrapped in a strip of paper to form a continuous round cylinder. The transfer device, which is the part of the machine situated between the two foregoing parts, and which is responsible for the transition or transfer of the rod between the porous band and the strip of paper conveyed by a continuous band disposed opposite the previous one, as well as for shaping the rod of tobacco into a cylinder of circular cross-section, is the part of interest within the scope of the present specification.
According to the prior art, this part of the machine includes a return-pulley for the porous band, usually a driving pulley, of relatively large diameter. Inasmuch as the .dumping beam is under negative pressure with respect to the ambient atmosphere in order to draw the tobacco onto the porous band, a certain air-tightness must be ensured at the end of it, especially at the location where the return-pulley is disposed. For that purpose, it is necessary to provide a mechanical part in the form of a shoe, a concave arcuate portion of which is applied at a short distance from the porous band disposed on the pulley; in order to keep a uniform distance between this shoe and the band, the shoe is adjustably attached to the dumping beam, downstream from the return-pulley.
Slightly upstream from the end of the dumping beam, on the top part of the frame of the machine facing the porous band and beneath the latter, another pulley guides another band carrying the strip of paper which is to surround the rod of tobacco. The strip of paper and the porous band approach one another for a certain distance as they travel, so that the strip of paper starts to drive the rod along at approximately the location where the latter leaves the porous band.
When the rod arrives opposite the axle of the return-pulley of the porous band, it is detached therefrom and enters under the air-tight shoe, guided by a longitudinal groove of semi-square cross-section disposed in the underside of the shoe. When the rod leaves the shoe, it is therefore in a substantially square shape, its top and side surfaces being formed by the sides of the longitudinal guide groove, whereas its bottom surface rests on the strip of paper supported by its conveying band.
After having passed the shoe, the rod of tobacco passes under a guide finger, the underside of which likewise comprises a longitudinal groove and which is adjustably attached to the bed of the machine; the strip of paper is wound about the rod of tobacco along this guide finger, thus carrying the rod along.
As stated above, the rod of tobacco is of substantially square cross-section when it leaves the shoe; after having passed the guide finger and been completely wound in the strip of cigarette paper, it is of circular cross-section, the transition between these two shapes having taken place under the guide finger. The longitudinal groove in the underside of this finger changes gradually from a semi-square cross-section to a semicircular cross-section and thus shapes the upper part of the rod, whereas the round shape of the lower part of the rod is produced when the strip of paper is applied to the rod. For proper shaping of the rod, it is absolutely necessary that the two successive longitudinal guide grooves of the shoe and of the guide finger be flawlessly aligned.
This prior art device comprises numerous drawbacks, particularly that of damaging the tobacco within the rod, for when the rod leaves the porous band and enters the guide groove of the shoe, its top and sides scrape forcefully against this groove; thereafter, when it passes through the guide groove of the guide finger, the rod changes from a square cross-section to a circular cross-section by compression of a significant part of its periphery. The friction of the shreds of tobacco against the shoe and the guide finger brings about extensive wear and tear on these parts, necessitating their frequent replacement. Moreover, because the top of the rod is braked by scraping against the grooves while the bottom part is being moved along by the strip of paper, an effect of longitudinal shear is produced on the rod, damaging the tobacco fibers and creating irregularities of longitudinal tobacco density within the rod, which may go so far as to tear the rod, as well as variations in the distance separating the regions of greater tobacco density intended to constitute the ends of the finished cigarette. This effect is further heightened by the fact that the transition between the advancing of the upper part of the rod by the porous band and the advancing of the lower part of the rod by the strip of paper on its carrier band takes place over a very short distance, even at a single point. Another drawback of the prior art device is that the groove for guiding the top part of the rod is situated on two separate elements, the shoe and the guide finger, each disposed on a separate element of the machine, and that these grooves must be carefully aligned with one another.